A Modeling approach for analysis and improvement of spindle-holder-tool assembly dynamics

The most important information required for chatter stability analysis is the dynamics of the involved structures, i.e. the frequency response functions (FRFs) which are usually determined experimentally. In this study, the tool point FRF of a spindle-holder-tool assembly is analytically determined by using the receptance coupling and structural modification techniques. Timoshenko’s beam model is used for increased accuracy. The spindle is also modeled analytically with elastic supports representing the bearings. The mathematical model is used to determine the effects of different parameters on the tool point FRF and to identify contact dynamics from experimental measurements. The applications of the model are demonstrated and the predictions are verified experimentally

Analytical prediction of part dynamics for machining stability analysis

An analytical procedure is developed to predict workpiece dynamics in a complete machining cycle in order to obtain frequency response functions (FRF) which are needed in chatter stability analyses. For this purpose, a structural modification method which is an efficient tool for updating FRFs is used. The removed mass by machining is considered as a structural modification in order to determine the FRFs at different stages of the process. The method is implemented in a computer code and demonstrated on different geometries. The predictions are compared and verified by FEA. Predicted FRFs are used in chatter stability analyses, and the effect of part dynamics on stability is studied. Different cutting strategies are compared for increased chatter free material removal rates considering part dynamics

models, EXperiments and high PERformance computing for Turbine mechanical Integrity and Structural dynamics in Europe (EXPERTISE)

Energy and Mobility are two primary driving forces in the 21st century. Development of incremental and disruptive technologies will have key impacts on the world’s societies, and on safety, security and competitiveness of Europe. Amongst those technologies, gas turbines will play a major role. Recovery of shale gas depends decisively on compressors. Modern gas supplied power plants are bridging towards the age of renewable energies. Aeroengines are to undergo the most massive changes in their history with the advent of composite materials, gear boxes, and turbine-electric concepts separating generation of power and thrust. A technological commonalities of the upcoming challenges is the need for full model based development and computer system simulation. There is agreement on this in the computational fluid dynamics (CFD) community. The structural dynamics and vibration questions are at present far from being addressed adequately. While US agencies and Asian powers have already started to prepare themselves, European research organisations and companies still seem to be too fragmented to reach critical research ressources and start corresponding initiatives. There are two main reasons for this. First, the physics of mechanical joining technologies that dominate the damping behavior of the large-scale structures under debate, are still poorly understood. Second, there is a lack of high performance computing (HPC) capabilities in structural dynamics, which goes back to the lack of knowledge of effective HPC technologies for structural dynamics. Since the US, China and India have started efforts in the field, we propose a European contribution through a Marie Curie ETN to allow a first generation of early stage researchers to catch up on the topics, ideally open up new fields of insight and approaches, and finally form a seed group for the upcoming challenges of the European turbine industry with respect to nonlinear structural dynamics and HPCMSCA-ITN-ETN - European Training Networks (H2020-MSCA-ITN-2016

Sinema kaçmaya kışkırtır:Bilmem anlatabildim mi?

Taha Toros Arşivi, Dosya No: 185/A-Sinema Tarihiİstanbul Kalkınma Ajansı (TR10/14/YEN/0033) İstanbul Development Agency (TR10/14/YEN/0033

A bazaar sustaining the function for 400 years: Spice Bazaar (Egyptian Bazaar) of Istanbul

Durhan, Sıla (Dogus Author) -- Conference full title: Sustainable Architecture and Urban Development : SAUD 2010, the Seventh International Conference of the Centre for the Study of Architecture in the Arab Region (CSAAR), Amman-JordanThe Spice Bazaar constructed in the 17th century, is the arasla of Yeni Mosque complex in Eminönü, in Historical Peninsula. It has surrounded by historical buildings such as a mosque, madrasah, tomb, commercial inns. The bazaar has always an extremely rote in the urban history at all times. By accommodating the city as a spice market, always largely spices or similar herbaI products have been sold in the bazaar. Thus, the bazaar has been always a shopping place that people prefer to go on purpose and also being belonged and committed to. Moreover, as apart of daily urban Iife, the bazaar is a welcoming point in Istanbul. Its large "L" block characterizes the Eminönü square in the view of Galata Bridge. But nowadays, the bazaar building is threatened by some adverse effects such as new additions closing its main façade, gift shops beginning to take herb and spice sellers' places and also underground roads that make it only a crossing point. Unfortunately these troubles cause the lack of relation with other historical heritages and the unhealthiness of the historical district. Only if, it would have better eonditions on the purpose of use and been increased the environmental life qualities, Egyptian Bazaar could have enriched the urban Iife. On the other hand, the building's urban life quality can be increased by noticing the value of the building physically, socially, economically, culturally and architecturally. Therefore, it must be succeeded that bazaar's and also historical heritage's sustainability by saving its original function as a spice bazaar

Evaluation of Nutritional Status in Turkish Adolescents as Related to Gender and Socioeconomic Status

Objective: To evaluate the nutritional status of Turkish high school adolescents using anthropometric indicators and to determine the relationship of nutritional status with gender and socioeconomic status (SES) in adolescents

Analytical modeling of spindle-tool dynamics on machine tools using Timoshenko beam model and receptance coupling for the prediction of tool point FRF

Regenerative chatter is a well-known machining problem that results in unstable cutting process, poor surface quality and reduced material removal rate. This undesired self-excited vibration problem is one of the main obstacles in utilizing the total capacity of a machine tool in production. In order to obtain a chatter-free process on a machining center, stability diagrams can be used. Numerically or analytically, constructing the stability lobe diagram for a certain spindleholdertool combination implies knowing the system dynamics at the tool tip; i.e., the point frequency response function (FRF) that relates the dynamic displacement and force at that point. This study presents an analytical method that uses Timoshenko beam theory for calculating the tool point FRF of a given combination by using the receptance coupling and structural modication methods. The objective of the study is two fold. Firstly, it is aimed to develop a reliable mathematical model to predict tool point FRF in a machining center so that chatter stability analysis can be done, and secondly to make use of this model in studying the effects of individual bearing and contact parameters on tool point FRF so that better approaches can be found in predicting contact parameters from experimental measurements. The model can also be used to study the effects of several spindle, holder and tool parameters on chatter stability. In this paper, the mathematical model, as well as the details of obtaining the system component (spindle, holder and tool) dynamics and coupling them to obtain the tool point FRF are given. The model suggested is veried by comparing the natural frequencies of an example spindleholdertool assembly obtained from the model with those obtained from a nite element software

Effect analysis of bearing and interface dynamics on tool point FRF for chatter stability in machine tools by using a new analytical model for spindle-tool assemblies

Self-excited vibration of the tool, regenerative chatter, can be predicted and eliminated if the stability lobe diagram of the spindle–holder–tool assembly is known. Regardless of the approach being used, analytically or numerically, forming the stability lobe diagram of an assembly implies knowing the point frequency response function (FRF) in receptance form at the tool tip. In this paper, it is aimed to study the effects of spindle–holder and holder–tool interface dynamics, as well as the effects of individual bearings on the tool point FRF by using an analytical model recently developed by the authors for predicting the tool point FRF of spindle–holder–tool assemblies. It is observed that bearing dynamics control the rigid body modes of the assembly, whereas, spindle–holder interface dynamics mainly affects the first elastic mode, while holder–tool interface dynamics alters the second elastic mode. Individual bearing and interface translational stiffness and damping values control the natural frequency and the peak of their relevant modes, respectively. It is also observed that variations in the values of rotational contact parameters do not affect the resulting FRF considerably, from which it is concluded that rotational contact parameters of both interfaces are not as crucial as the translational ones and therefore average values can successfully be used to represent their effects. These observations are obtained for the bearing and interface parameters taken from recent literature, and will be valid for similar assemblies. Based on the effect analysis carried out, a systematic approach is suggested for identifying bearing and interface contact parameters from experimental measurements

Selection of design and operational parameters in spindle-holder-tool assemblies for maximum chatter stability by using a new analytical model

In this paper, using the analytical model developed by the authors, the effects of certain system design and operational parameters on the tool point FRF, thus on the chatter stability are studied. Important conclusions are derived regarding the selection of the system parameters at the stage of machine tool design and during a practical application in order to increase chatter stability. It is demonstrated that the stability diagram for an application can be modified in a predictable manner in order to maximize the chatter-free material removal rate by selecting favorable system parameters using the analytical model developed. The predictions of the model, which are based on the methodology proposed in this study, are also experimentally verified

Investigating dynamics of machine tool spindles under operational conditions

Chatter is one of the major problems in machining and can be avoided by stability diagrams which are generated using frequency response functions (FRF) at the tool tip. During cutting operations, discrepancies between the stability diagrams obtained by using FRFs measured at the idle state and the actual stability of the process are frequently observed. These deviations can be attributed to the changes of machine dynamics under cutting conditions. In this paper, the effects of the cutting process on the spindle dynamics are investigated both experimentally and analytically. The variations in the spindle dynamics are attributed to the changes in the bearing parameters. FRFs under cutting conditions are obtained through the input-output relations of the cutting forces and the vibration response which are measured simultaneously. Experimentally and analytically obtained FRFs are then used in the identification of the bearing parameters under cutting conditions. Thus, bearing properties obtained at idle and cutting conditions are compared and variations in their values are obtained